The present invention relates to a method of manufacturing a magnetic recording medium having a lubricant topcoat exhibiting improved tribological performance and reduced stiction failures. The present invention has particular applicability in manufacturing magnetic recording media suitable for high density recording and long term magnetic performance stability.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a xe2x80x9chead crash.xe2x80x9d Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as xe2x80x9ctexturing.xe2x80x9d Conventional texturing techniques include laser texturing the surface of a non-magnetic substrate to provide a textured landing zone in which a magnetic head can land when the drive is not in use, and can take off when the drive is reading and writing data. Typically, the surface of the non-magnetic substrate is polished to a specular finish prior to laser texturing to form the landing zone leaving a substantially smooth data zone. Subsequently, an underlayer, a magnetic layer, a protective overcoat and a lubricant topcoat are sequentially deposited, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers. Typical substrate materials include an aluminum alloy with a layer of amorphous nickel phosphorous thereon, glasses, ceramics and glass-ceramic materials, as well as graphite. Underlayers typically comprise chromium or a chromium alloy, while the magnetic layer typically comprises a cobalt based alloy. Protective overcoats typically contain carbon. Such layers are typically deposited by sputtering techniques preformed in an apparatus containing sequential deposition chambers.
In accordance with conventional practices, a lubricant topcoat is uniformly bonded to the protective overcoat. The lubricant topcoat applied to the protective overcoat performs several functions. The lubricant topcoat improves tribological performance for reduced friction, stiction and crash rate at the heat-disk-interface. In addition, a lubricant topcoat prevents wear between the disk and head interface during drive operation. Excessive wear of the protective overcoat increases friction between the head and disk, thereby causing catastrophic drive failure. In addition, the lubricant topcoat prevents the protective overcoat from corrosion and other damage, thereby providing long-term magnetic performance stability.
Excess lubricant at the head-disk interface causes high stiction between the head and disk. If stiction is excessive, the drive cannot start and catastrophic failure occurs. Accordingly, the lubricant thickness must be optimized for stiction and friction.
Conventional employed lubricants include perfluoro polyethers (PFPEs) which are long chain polymers composed of repeat units of a small perfluoronated aliphatic oxides, such as perfluoroethylene oxide or perfluoropropylene oxide. PFPEs typically provide excellent lubricity, a wide liquid-phase temperature range, low vapor pressure, small temperature dependence of viscosity, high thermal stability and low chemical reactivity. PFPEs also exhibit low surface tension, resistant to oxidation at elevated temperatures, low toxicity and moderately high solubility for oxygen. Various PFPE polymers are commercially available, such as Fromblinz, Fromblinz Y including Z-dol and am2001 from Montedison and Demnum from Daikin.
A typical lubricant coating comprises a bonded lube layer and a mobile lube layer thereon. The bonded lube layer contains lubricant molecules which are chemically or physically bonded to the overcoat, i.e., carbon, on the disk. The bonded lubricant molecules can not be removed by washing with a solvent as can the mobile lube layer. Bonding assists in reducing lubricant which can be lost due to spin off, evaporation or chemical displacement. It has been theorized that a bonded lube layer contributes to lower stiction forces. The mobile lube layer contains molecules that are not bonded and can be easily removed with an appropriate solvent.
Conventional practices in texturing the substrate, e.g., a non-magnetic substrate or underlayer provided thereon, comprise decoupling the magnetic requirements (data zone on which information is recorded and read) from the mechanical requirements (landing zone), by forming a dedicated landing zone where the slider is parked and lands after the drive has been shut down. Adverting to FIG. 1, a conventional magnetic recording disk 10 for a Winchester hard-drive design comprises an inner annular landing zone 11 and an outer annular data zone 12. As a result of such zone design, the thickness of the lubricant topcoat is typically optimized for improved tribological performance and reduced friction, stiction and crash rate at the head-disk interface. Accordingly, the thickness required for the landing zone, which undergoes a large number of head-disk contacts, is required to be greater than the thickness of the lubricant topcoat overlying the data zone, where only a thin continuous lubricant layer is required to prevent corrosion and damage to the underlying protective overcoat thereby ensuring long-term magnetic performance stability.
However, conventional methods for forming a lubricant topcoat in the magnetic media industry, such as xe2x80x9cdip-lubexe2x80x9d, xe2x80x9cvapor-lubexe2x80x9d and xe2x80x9cspray-lubexe2x80x9d, are only capable of forming a lubricant topcoat at a substantially uniform thickness across the entire disk surface without differentiating the lubricant thickness between the different radial zones, i.e., landing zone and data zone. The conventional practice of depositing a lubricant topcoat at a uniform thickness overlying both the data zone and landing zone is problematic. For example, upon applying a thick lubricant topcoat for improved tribological performance, fly-stiction occurs as a result of lubricant transferred to the head when it flies over the data zone, and lubricant is transferred from the head to the head-disk interface when it rests at the landing zone, thereby causing stiction failure.
Eltoukhy et al. in U.S. Pat. No. 5,674,582 disclose a method of manufacturing a thin film disk media with differential lubricant thicknesses by initially applying a lubricant area and then buffing the lubricant over the data area as to provide a substantially reduced lubricant layer overlying the data zone for improved friction. Wei et al. in U.S. Pat. No. 5,820,945 disclose a magnetic disk having a zone of different lubricant thickness, such as lubricant-free, bonded-only or mostly-bonded, covering a different portion of the disk, such as over the data zone. In copending U.S. patent application Ser. No. 09/311,366 filed on May 13, 1999 now U.S. Pat. No. 6,221,442B1, a method is disclosed for reducing the lubricant thickness over the data zone using a laser light beam. The entire disclosure of copending U.S. patent application Ser. No. 09/311,366 (U.S. Pat. No. 6,221,442B1) is hereby incorporated by reference herein.
Conventional practices further seek to enhance topological performance by initially treating a raw lubricant containing a relatively broad molecular range distribution by supercritical fluid extraction (SFE) and then applying such a treated lubricant, e.g., a PFPE lubricant, to a magnetic disk structure, e.g., on the carbon-containing overcoat. For example, Zdol-2000 available from Ausimont, exhibits a relatively broad molecular weight distribution of about 900 to about 10,000 and, hence, does not satisfy the rigid tribological performance requirements for current magnetic media wherein the head to media spacing is significantly reduced for higher storage densities, e.g., less than about 100 xc3x85. Accordingly, such lubricants are initially subjected to SFE, whereby the molecular range distribution is reduced by about 30%, e.g., to about 3,000xc2x1200. Unfortunately, the use of lubricants previously subjected to SFE is extremely costly due to low yield and, hence, the lubricant cost is increased by about 2 to 15 times of the raw lubricant.
Accordingly, there exists a need for an efficient, cost-effective method of manufacturing a magnetic recording medium with a lubricant topcoat exhibiting improved tribological performance and fly-stiction.
An advantage of the present invention is an efficient cost-effective method of manufacturing a magnetic recording medium having a lubricant topcoat optimized for tribological performance with reduced fly-stiction.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a method of manufacturing a magnetic recording medium, the method comprising: applying a lubricant having a broad molecular weight distribution to form a lubricant coating having a first thickness on a surface of a composite containing a magnetic layer on a non-magnetic substrate, the surface of the composite having a landing zone and data zone; and treating the applied lubricant coating with a laser light beam to effect in-situ fractionation, thereby reducing the molecular weight distribution of the lubricant.
Embodiments of the present invention comprise applying a PFPE lubricant having a relatively broad molecular weight distribution, e.g., about 500 to about 15,000, to a carbon-containing protective overcoat and treating the applied PFPE lubricant with a laser light beam to reduce the molecular weight distribution by about 30%, e.g., to about 3,500xc2x1100. Embodiments of the present invention further include treating the deposited lubricant to reduce the thickness over the data zone with respect to the thickness of the lubricant coating over the landing zone. Embodiments of the present invention further include treating the deposited lubricant with a laser light beam to increase the thickness of the deposited bonded lube layer by no less than about 100%.
Additional advantages of the present invention will become readily apparent to those having ordinary skill in the art from the following detailed description, wherein the embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.